Variable displacement pump

ABSTRACT

A pump chamber  18  is formed between a cam ring  17  and a rotor  15  in a pump body  11 . The cam ring is formed so as to move to direction that pump capacity of the pump chamber increases and decreases. A first and second fluid pressure chambers  33  and  34  are formed at both sides of moving direction of the cam ring  17 . The pump has a spool operates to axis direction by difference in fluid pressure of upper and lower stream sides of a metering throttle  50  formed on a way of a discharge side passage  27  of the pump chamber and provides at least a control valve  30  controlling fluid pressure in the first fluid pressure chamber. An electronic driving unit applying thrust to axis direction to the spool of the control valve, for example, a solenoid  60  is provided.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a variable displacement pump used for power steering system (apparatus using pressure fluid) as an oil pressure source (fluid pressure source) to obtain auxiliary steering power lightening the power of steering wheel of vehicle for example.

[0003] 2. Description of the Related Art

[0004] In the pump used for power steering system, it is desired that pressure fluid of enough quantity to obtain auxiliary steering power corresponding to steering state at steering operation of steering wheel (so called at steering) is applied to a power cylinder of power steering system. Contrary to this, at non-steering such as straight travel of vehicle, supplying the pressure fluid is actually needless.

[0005] Moreover, in the pump used for power steering system, it is desired that supplying quantity of pressure fluid at high speed travel is less than at middle or low speed travel and travel stability at high speed straight travel is kept with rigid feeling of steering wheel at high speed travel.

[0006] A positive displacement pump driven by engine of vehicle is generally used as this kind of pump for power steering system. The positive displacement pump has characteristic that discharge flow rate increases as revolution cycle of the engine increases. Therefore, to use the positive displacement pump as the pump for power steering system, a flow control valve is indispensable, which controls discharge flow rate from the pump within definite quantity independently of the revolution cycle. However, in the positive displacement pump having such the flow control valve, load to the engine does not decreases even if a part of pressure fluid is returned to a tank through the flow control valve, and save energy effect is not obtained because driving horse power of the pump is same.

[0007] To solve such bad condition, variable displacement vane pumps decreasing discharge flow rate per one revolution of the pump (cc/rev) in proportion of decrease of revolution cycle have been proposed by Japanese Patent Laid-Open No. 200883/1994, Japanese Patent Laid-Open No. 243385/1995, and Japanese Patent Laid-Open No. 200239/1996. These variable displacement pumps are so called engine revolution cycle sensitive pump, and discharge flow rate of the pump can be decreased because the cam ring is moved to direction which pump capacity of the pump chamber decreases corresponding to magnitude of fluid pressure of discharge side of the pump when engine revolution cycle (pump revolution cycle) increases.

[0008] Such the variable displacement pump can make light steering obtaining large auxiliary steering power at steering while stop or low speed travel because discharge flow rate of the pump is increased relatively when engine revolution cycle is small even at stop or low speed travel of the vehicle. Since the engine revolution cycle becomes large and discharge flow rate of the pump becomes small relatively at high speed travel of vehicle, steering having moderate rigid feeling at steering operation power while high speed travel becomes possible.

[0009] Although discharge quantity following engine revolution cycle is obtained at use as oil pressure source of a power steering system in this kind of variable displacement pump, other condition, for example, condition change of steering state such as speed of vehicle, steering speed, steering angle and etc. has not been considered past. Therefore, there are bad conditions as the followings.

[0010] Since the conventional variable displacement pump is so called an engine revolution cycle sensitive type, engine revolution cycle becomes high at acceleration, up slope, and down slope even while low speed travel so that discharge flow rate from the pump decreases. At steering operation while such low speed travel, necessary flow rate is not kept in the power steering system because of very few discharge quantity of pump so that there is the possibility lack of auxiliary steering power. Because of that, in the conventional pump, flow rate is not so decreased in order to keep necessary flow rate.

[0011] Therefore, the conventional variable displacement pump has a limit to decrease discharge flow rate from the pump when engine revolution cycle increases, and effect is not enough that supplying fluid rate necessary for steering operation as the variable displacement pump is obtained and plan saving energy.

[0012] According to this kind of variable displacement pump, it is desired at point of saving energy that designated auxiliary steering power is obtained by supplying pressure fluid of designated flow rate at steering (when steering is need) and supplying flow rate of pressure fluid is made almost zero or necessary minimum at non-steering (when steering is needless). For example, when the variable displacement pump is directly driven with engine of the vehicle, discharge quantity from the pump is needless at non-steering even when engine revolution cycle is large, and driving horse power of the pump is depressed by decreasing discharge quantity of the pump of this time. Considering this point is desired.

[0013] When this kind of variable displacement pump is controlled, it is desired to carry out the most suitable pump control according to travel state of the vehicle judging whether the vehicle stops, travels with low speed, middle speed, or high speed, and whether steering is carried out at each travel, or non-steering. Therefore, it is need that such travel state and steering state of the vehicle are surly grasped and performance as a power steering system is shown carrying out pump control suitably. Further it is need to take some measures to obtain saving energy effect as the variable displacement pump adding operating state of the pump and travel state of the vehicle by carrying out driving control of the pump at designated condition.

SUMMARY OF THE INVENTION

[0014] The invention is carried out in view of such the situation. An object of the invention is to obtain a variable displacement pump that pressure loss of a throttle part provided at a discharge side passage is decreased without response delay when operation of power steering system being apparatus using pressure fluid, for example, auxiliary steering power is necessary, and that necessary and enough flow rate is supplied. Further, the variable displacement pump can decrease power consumption at driving the pump, and shows the maximum saving energy effect, and has high reliability.

[0015] Another object of the invention is to obtain a variable displacement pump in which it is an oil pressure pump for vehicle and comfortable steering feeling is obtained by controlling corresponding to travel condition such as speed of vehicle, steering speed and etc. at using for oil pressure source of a power steering system. Further, the variable displacement pump can more show saving energy effect by decreasing discharge flow rate as soon as possible at non-steering while straight travel of vehicle, discharge quantity of the pump is instantly decreased to necessary quantity when steering is requested, and designated auxiliary steering power is kept.

[0016] To meet such the object, a variable displacement pump according to the invention comprises: a pump body holding a cam ring formed between the cam ring and a rotor so as to move to direction that pump capacity of the pump chamber increases and decreases and forming a first and a second fluid pressure chambers at both sides of moving direction of the cam ring; a spool operating to axis direction by difference in fluid pressure of upper and lower stream sides of a metering throttle formed on the way of a discharge side passage of the pump chamber; and a control valve controlling at least fluid pressure in the first fluid pressure chamber; wherein an electronic driving unit applying thrust to axis direction to the spool of the control valve is provided.

[0017] According to the invention, by applying forcibly thrust to axis direction to the spool of the control valve operating the electronic driving unit in response to necessity at steering required for example, the control valve is electrically controlled adding to usual fluid pressure control and the cam ring is instantly moved moreover in designated state by fluid pressure in fluid pressure chamber obtained from the result.

[0018] That is, according to the invention, the spool of the control valve is positioned at designated place of axis direction with balancing of difference in upper and lower stream sides of the metering throttle formed on the way of the pump discharge side passage and fluid pressure energizing force of energizing unit energizing the spool to one direction, and discharge flow rate of pressure fluid from the pump chamber can be kept minimum. When thrust to axis direction acts to the spool by the electronic driving unit, discharge flow rate of pressure fluid from the pump chamber can be increased to desired value by connecting the pump suction side to the first fluid pressure chamber for example and connecting fluid pressure of the lower stream side of the metering throttle to the second fluid pressure chamber.

[0019] By selectively connecting fluid pressure of the upper stream side of the metering throttle and the pump suction side to the first fluid pressure chamber and connecting fluid pressure of the lower stream side of the metering throttle and the pump suction side to the second fluid pressure chamber in the above-mentioned control valve, difference in fluid pressure between the first and second fluid pressure chambers for moving the cam ring can be made large, and moving and displacement of the cam ring are surly carried out in response of necessity.

[0020] The variable displacement pump according to the invention has further comprises an electronic control unit driving and controlling the electronic driving unit, wherein the electronic control unit has a steering sensor detecting steering speed of a steering wheel and drives and controls the electronic driving unit according to a signal from the steering sensor in the variable displacement pump.

[0021] The variable displacement pump according to the invention has further comprises an electronic control unit driving and controlling the electronic driving unit, wherein the electronic control unit has a steering sensor detecting steering speed of a steering wheel and a speed sensor detecting travel speed of vehicle, and drives and controls the electronic driving unit according to a signal from these each sensor in the variable displacement pump.

[0022] According to the invention, a variable displacement pump used for fluid pressure source of power steering system has necessary minimum flow rate at usual straight travel without steering operation while travel of vehicle. When auxiliary steering power by power steering system is necessary, it is possible to operate the electronic driving unit corresponding to steering speed or steering speed and speed of vehicle by the electronic control unit and to keep instantly enough flow rate of the pump discharge side.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 shows a variable displacement pump of an embodiment according to the invention and is a construction view to describe a fluid pressure circuit construction using the pump.

[0024]FIG. 2 is a side section view showing a cut main part of the variable displacement pump in FIG. 1.

[0025]FIG. 3 is a main enlarged section view enlarging a control valve part of the variable displacement pump in FIG. 1.

[0026]FIG. 4 is a main enlarged section view when the valve part is moved to balance state from non-operation state of FIG. 3.

[0027]FIG. 5 is a main enlarged section view showing state when the maximum flow rate is discharged from FIG. 3 and FIG. 4.

[0028]FIG. 6 is a characteristic view showing supplying flow rate characteristic at non-steering (at straight travel) and steering vs. speed when the variable displacement pump according to the invention is used for fluid pressure source of power steering system.

[0029]FIG. 7 is a characteristic view showing supplying flow rate characteristic vs. steering speed when the variable displacement pump according to the invention is used for fluid pressure source of power steering system.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0030] FIGS. 1 to 3 are views showing an embodiemnt of a variable displacement pump according to the invention. In the embodiment, it is described that the variable displacement pump according to the invention is used for a vane type oil pump of being oil pressure generating source of a power steering system.

[0031] In FIG. 1 and FIG. 2, a vane-type variable displacement pump shown with symbol 10 has a front body 11 and a rear body 12 constructing a pump body. The front body 11 has a cup shape at the whole thereof, a storage space 14 storing and arranging pump composing elements as a pump cartridge is formed at the inside thereof, and the rear body 12 is assembled being combined so as to block the opening end of the storing space 14.

[0032] At the front body 11, a driving shaft 16 to drive to rotate a rotor 15 constructing the pump composing elements from the outside is supported rotatably in the penetrating state. The rotor 15 rotates counterclockwise in FIG. 1.

[0033] Symbol 17 is a cam ring, the cam ring 17 has an inside cam face 17 a arranged inserting into an outer circumference portion of the rotor 15 having vanes 15 a, and a pump chamber 18 is formed between the inside cam face 17 a and the rotor 15. The cam ring 17 is positioned at biased state with the rotor 15, and an almost crescent-shaped space formed between the cam ring 17 and the rotor 15 defines the pump chamber 18. The cam ring 17 is arranged reciprocatably in an adapter ring 19 formed in fitting state at space inner wall part in the storage space 14 so as to vary capacity (pump capacity) of the pump chamber 18 as described below. Symbol 17 b is a compression coil spring pressing the cam ring 17 to direction that pump capacity of the pump chamber 18 becomes maximum.

[0034] In FIG. 2, symbol 20 shows a pressure plate. The pressure plate 20 is arranged being laminated with contact pressed to the front body 11 side of the pump cartridge (pump composing elements) constructed by the above-mentioned rotor 18, cam ring 17, and adapter ring 19. At opposite side face of the pump cartridge, the end face of the rear body 12 is contacted being pressed as a side plate, and the front body 11 and the rear body 12 are assembled integratedly.

[0035] The pressure plate 20 and the rear body 12 being the side plate laminated through the cam ring 17 are assembled integratedly at the state positioned by a reciprocation fulcrum pin 21 in revolution direction. The reciprocation fulcrum pin 21 functions as a shaft fulcrum portion and a positioning pin capable of reciprocation of the cam ring 17 and as sealing material defining fluid pressure chamber reciprocating the cam ring 17.

[0036] Symbols 22 and 23 are a pump suction side opening and a pump discharge side opening opened at the pump chamber 18, these openings 22 and 23 are formed by almost arc shape groove portion, and are opened at a pump suction side area of a start side and a pump discharge side area of an end side of revolution direction of the rotor 15 as shown in FIG. 1. The suction side opening 22 is provided concavely at an end face facing the pump chamber 18 of the rear body 22, and the discharge side opening 23 is provided concavely at an end face of the pump chamber 18 side of the pressure plate 20 as shown in FIG. 1.

[0037] At the rear body 12, a suction side passage 25 supplying suction side fluid sucked from a tank T to the suction side opening 22 through a suction port is formed. The suction side fluid sucked from the tank T (pump suction side) passes the pump suction side passage 25 in the rear body 12 from the suction port and is supplied into the pump chamber 18 from the suction side opening 22 opening at end face of the rear body 12. Symbol 25 a is a pump suction side passage opening at center part of a valve hole 31.

[0038] At front side of the pressure plate 20 of the front body 11, a pressure chamber 26 of almost arc-shaped pump discharge side is formed around the driving shaft 16. The pressure chamber 26 is connected to a discharge port 27 a through a pump discharge side passage 27 formed in the front body 11 and discharges discharge side fluid pressure guided to the pressure chamber 26 from the discharge port 27 a.

[0039] Symbol 30 is a control valve comprising the valve hole formed to perpendicular direction to the shaft 16 at upper side of the front body 11 and a spool 32. The control valve is operated by thrust to axis direction applied by difference in pressure between upper stream and lower stream of a metering throttle 50 provided at a part of the pump discharge side passage described below and a solenoid 60 provided as an electronic driving unit. The control valve 30 controls fluid pressure in a first and second fluid pressure chambers 33 and 34 formed at both sides of the cam ring 17 being separated by sealing material 35 provided at the reciprocation fulcrum pin 21 and the symmetrical position with respect of the axis in the adapter ring 19 as shown in FIG. 1 and FIG. 3.

[0040] At one end of the valve hole 31, a chamber is formed where fluid pressure of the pump discharge side is connected to a pilot pressure passage 41 from the pressure chamber 26 and fluid pressure P1 of upper stream side of the metering throttle 50 is conducted.

[0041] At other side of the valve hole 31, a spring chamber is formed which has a compression coil spring 36 a energizing the spool 32 to the one end. The spool 32 is energized to left side in FIG. 2. In the spring chamber 36, fluid pressure P2 of lower side of the metering 50 formed between the pump discharge side passage 27 and an apparatus using pressure fluid (here, a power cylinder PS of a power steering system) is conducted by a pilot pressure passage 42.

[0042] At inside of the spool 32, a relief valve 49 is provided.

[0043] On the way of the pilot pressure passage 42, a pilot throttle 42 a may be provided as shown with a doted line in FIG. 3. By providing the pilot throttle 42 a, bad influence such as fluid pressure change and the like to the spool 32 of the control valve 30 can be prevented. The pilot throttle 42 a makes fluid pressure in the spring chamber 36 of the control valve 30 decrease at relief of the relief valve 49 formed in the spool 32. Since the cam ring 17 reciprocates to direction that capacity of the pump chamber 18 by operation of the control valve 30 caused by the pressure decrease, pump discharge quantity decreases so as to become advantage to save energy of the pump.

[0044] The spring chamber 36 is connected to a connecting passage 37 to the second fluid pressure chamber 34 when the spool 32 is placed at position of FIG. 1 and FIG. 3. When the spool 32 moves to the spring chamber 36 side (right side in the figure), the spool 32 is gradually separated from the second fluid pressure chamber 34 and is connected to a pump suction side chamber 30 a defined by ring-shaped groove formed at center part of axis direction of the spool 32 through a gap passage defined by a small diameter portion 32 d formed at a land portion 32 c of one end side of the spool 32. Therefore, to the second fluid pressure chamber 34, fluid pressure P2 of lower stream side of the metering throttle 50 and fluid pressure of the pump suction side are supplied selectively through the spring chamber 36 and the pump suction side chamber 30 a with the moving of the spool 32. At a part of the above-mentioned connecting passage 37, a damper throttle 37 a is formed.

[0045] The pilot pressure passage 42 is connected to the spring chamber 36 through a hole portion 70 a and an inner hole 70 b formed at a part of a plug member 70 described below.

[0046] A high pressure side chamber 38 formed at one end side of the spool 32 is closed at non-operation, that is, when the spool 32 is placed at position of FIG. 1 and FIG. 3, and the connecting passage 39 is connected to the pump suction side chamber 30 a through the gap passage defined by the small diameter portion 32 b formed at the land portion 32 a of one end side of the spool 32.

[0047] Since fluid of discharge side is supplied into the chamber 38 through the pilot pressure passage 41 when the pump 10 starts, the spool 32 moves to the spring chamber 36 side (right side in the figure) and the spool 32 is gradually separated from the pump suction side and is connected to the first fluid pressure chamber 33 through the connecting passage 39. Therefore, to the first fluid pressure chamber 33, fluid pressure of the pump suction side and fluid pressure P1 of upper stream side of the metering throttle 50 are supplied selectively through the pump suction side chamber 30 a and the high pressure side chamber 38 with the moving of the spool 32. At a part of the connecting passage 39, a damper throttle 39 a is formed.

[0048] By using the above-mentioned control valve 30, fluid pressure of the pump suction side is conducted to at least any of fluid pressure chambers 33 and 34 formed at both sides of moving direction of the cam ring 17 in spite of small operation power (operation pressure caused by difference in pressure and solenoid thrust) of the valve so as to make operation pressure. Therefore, a certain moving displacement of the cam ring is obtained because difference in fluid pressure between the fluid pressure chambers 33 and 34 is made large.

[0049] Since difference in fluid pressure (differential pressure) is small at upper and lower stream sides of the metering throttle 50 just after the pump starts in the above-mentioned control valve 30, the spool 32 is placed at the position shown in FIG. 1 and FIG. 3, and the first fluid pressure chamber 33 is connected to the pump suction side so that fluid pressure P0 is conducted. On the other hand, to the second fluid pressure chamber 34, fluid pressure P2 of the pump discharge side at the lower stream side of the metering throttle 50 is conducted so that the cam ring 17 is in the sate that capacity of the pump chamber 18 becomes maximum.

[0050] When discharge flow rate from the pump chamber 18 increases and differential pressure at upper and lower stream sides of the metering throttle 50 increases to designated differential pressure controlled by fixed throttle of the metering throttle 50, the spool 32 moves to direction that the spring 36 a is compressed (the spring chamber 36 side) and thereby balance is kept at the designated position as shown in FIG. 4. At that time, the spool 32 becomes almost stable in the state that the pump suction side is connected or is able to be connected to the first and second fluid pressure chambers 33 and 34 of both sides of the cam ring 17.

[0051] In such the balancing state of the spool 32, the cam ring 17 moves to right side in the figure by differential pressure between both fluid pressure chambers 33 and 34 and energizing force of the compressed coil spring 17 b and keeps balance at the position that the pump chamber 18 becomes the minimum pump capacity. In the state, the pump 10 has the minimum pump discharge quantity, for example, 4 l/min. This value is suitably set by fixed throttle quantity of the metering throttle 50, capacity of the pump chamber 18 and etc. from necessary minimum auxiliary steering power.

[0052] In the above vane-type variable displacement pump 10, almost all constructions and operation states are well known from past, so the concrete description is omitted. The fundamental pump construction of the variable displacement pump 10 is almost same as disclosed in Japanese Patent Laid-Open No. 200883/1994 and Japanese Patent Laid-Open No. 200239/1996.

[0053] According to the invention, in the variable displacement pump 10, a solenoid 60 is added as an electronic driving unit applying thrust of axis direction to high pressure side chamber 38 side from the spring chamber 36 side at the spool 32 of the control valve 30.

[0054] For the electronic control unit of the solenoid 60, a CPU 61, a driving circuit 62, a speed sensor 63, and a steering sensor 64 are provided.

[0055] In detail, a screw hole is provided at the spring chamber 36 side of the control valve 30, and the plug member 70 is screwed into the screw hole to fix. At outer end of the plug member 70, the solenoid 60 is attached in the state that a solenoid rod 65 appears. The solenoid rod 65 is assembled at end portion of the spring chamber 36 side of the spool 32, and faces to tip end of a rod 71 a of a rod member 71 held reciprocatingly at inner end side of the plug member 70.

[0056] Although these rods 65 and 71 a face with designated gap at non-operating state of the pump 10 as shown in FIG. 1 and FIG. 3, the both face so as to contact as shown in FIG. 4 when the pump operates.

[0057] In such the construction, the condition shown in FIG. 4 is kept at non-operation state and discharge flow rate from the pump 10 is the minimum flow rate controlled the metering throttle 50. At this time, the solenoid is kept in non-conductive state.

[0058] In such balance state, pump discharge flow rate corresponding to speed of the vehicle, steering speed and etc. is obtained when steering is required. That is, designated current flow through the solenoid 60 by that signals from sensors 63 and 64 pass through the CPU 61 and the driving circuit 62. The rod 65 applies thrust to the spool 32 through the rod member 71 to left direction in the figure as shown in FIG. 4. Then, the spool 32 moves to left side in the figure corresponding to thrust based on the magnitude of passing current and the first fluid pressure chamber 33 is connected to the pump suction side (P0. The second fluid pressure chamber 34 is connected to fluid pressure P2 of lower stream side of the metering throttle 50, thereby the cam ring 17 moves to left side in the figure so as to make capacity of the pump chamber 18 large. Therefore, discharge quantity from the pump 10 is increased by value controlled by the above-mentioned electronic control unit (symbols 61 to 64).

[0059] An example of such flow rate characteristic is shown in FIG. 6. Here, a thick solid line shows the minimum flow rate of the variable displacement pump 10 according to the invention (for example, 4 l/min), and a thin solid line is the maximum flow rate necessary at quick steering (for example, 7 l/min). These are certain flow rates without influence of speed of the vehicle.

[0060] When the speed changes, the flow rate characteristic is shown in FIG. 6 depending on steering speed (deg/sec).

[0061] By controlling so as to obtain such flow rate characteristic, the spool 32 of the control valve 30 moves so as to keep the minimum flow rate (for example, 4 l/min) controlled by the metering throttle 50 and keeps the state at non-steering. Since the spool 32 is kept in balance state with the minimum flow rate at non-steering, differential pressure at the metering throttle 50 can be set small. Therefore, pressure loss at the metering throttle 50 is small. Since the solenoid 60 is in non-conductive state in this time, power consumption driving the pump 10 can be reduced and power consumption of electronic control system can be reduced.

[0062] On the other hand, at steering, it is carried out instantly that the spool 32 is moved directly to left side in the figure, from the state of FIG. 4 to the state of FIG. 5, by thrust generating corresponding to current value flowing through the solenoid 60. Thus, it is possible to control fluid pressure of the first and second fluid pressure chambers 33 and 34 and to generate designated auxiliary steering power increasing quickly the pump discharge quantity to the designated flow rate. Therefore, it is possible to generate the designated auxiliary steering power and to keep performance as a power steering system without response delay even at quick steering.

[0063] In other words, according to the construction of the above-mentioned invention, auxiliary steering power can be suitably operated when steering operation is necessary independent of travel state by controlling flow rate of pressure fluid applied from the variable displacement pump to power steering system corresponding to travel condition of the vehicle such as speed of vehicle, steering speed and the like. Further, since the solenoid 60 is in the non-conductive state at non-steering such as straight travel, the spool 32 of the control valve 30 keeps the balance state of FIG. 4. Since pump discharge flow rate is kept minimum as above-mentioned in this balance state and differential pressure to keep the minimum flow rate at this state is small, pressure loss at the metering throttle 50 is small. Therefore, large saving energy effect is expected in the variable displacement pump 10 according to the invention like this. That is, by adopting sensing type of speed of vehicle and steering speed using electronic control together, it is possible to obtain comfortable steering feeling and saving energy effect.

[0064] Here, at the control apparatus in the above-mentioned variable displacement pump 10, conversion tables of speed of vehicle vs. current and steering speed vs. current to control passing current through the solenoid 60 corresponding to signals from the speed sensor 63 and the steering sensor 64 are provide in the CPU 61 being the electronic control unit and current control is carried out corresponding thereto. The detailed description is omitted.

[0065] In short, the spool 32 of the control valve 30 is kept in balance state with difference in fluid pressure so as to be flow rate controlled by the metering throttle 50 and the minimum flow rate is discharged in this state at non-steering in the variable displacement pump 10. At this time, it can be set so as to keep suitable minimum flow rate even at steering such as keeping steering at turning travel and correcting steering. Further, it is possible that response delay does not occur when flow rate is increased from the minimum flow rate set like this at quick steering.

[0066] By making the solenoid 60 non-conductive state at non-steering, making the solenoid 60 conductive state to generate solenoid thrust at steering required, and moving the spool 32 by a resultant force with spring force, power consumption is usefully made minimum.

[0067] Further, by controlling the control valve 30, power consumption to drive the pump as the variable capacitor pump 10 is made minimum and it is possible to improve saving energy effect.

[0068] In the above-mentioned control valve 30, if section area of the spool 32 is 1.33 cm² for example, differential pressure at the metering throttle 50 is 0.07 MPa when solenoid thrust is ON at non-steering and the minimum flow rate of 4 l/min is obtained. Because force by the differential pressure and spring force 9.29 N are balanced, the spool 32 becomes balance state.

[0069] On the other hand, when current flows through the solenoid 60 and solenoid thrust 17.26 N acts while quick steering, the spool 32 moves to left direction in the figure. After that, force by differential pressure at the metering throttle 50, solenoid thrust, and spring force are balanced. At this time, differential pressure is 0.2 MPa and maximum flow rate 7 l/min is obtained.

[0070] In the above-mentioned structure, solenoid thrust is removed when electronic control is defective because any of elements constructing the electronic control unit. However, even at this time, the spool 32 is kept at position of the balance state acting by differential pressure between upper and lower sides of the metering throttle 50, therefore, pump discharge quantity of the minimum flow rate previously set and necessary minimum steering performance can be kept.

[0071] The invention is not limited in the structure described in the embodiment and it is needless to say that shape and construction of each part can be suitably deformed and changed.

[0072] Although minimum flow rate supplied from the pump is 4 l/min for example in the embodiment, smaller flow rate than the above may be set without the limitation if steering power is enough adding travel condition such as speed of vehicle and steering speed.

[0073] In the embodiment, driving current to solenoid 60 is controlled by that the CPU 61 and the driving circuit 62 are used as the electronic control portion to control the electronic driving unit such as the solenoid and the like and speed of vehicle from the speed sensor 63 and steering speed from the steering sensor 64 are input to the CPU 61 as input signals. However, the invention is not limited to this, and discharge flow rate of the pump may be controlled adding various travel conditions vehicle, from revolution cycle of engine, steering angle, steering direction, axle load down.

[0074] For example, as shown in FIG. 7, driving current to the solenoid 60 being the electronic driving unit is controlled using steering speed from the steering sensor 64 as input signal, it may be constructed that the solenoid is in non-conductive state at non-steering and the solenoid is in conductive state at steering. Of course, the invention is not limited to control to take only steering speed as input signal.

[0075] Although the electronic driving unit is the solenoid 60 for example, the electronic driving unit is not limited to this and may be a unit constructing a driving apparatus such as an electromagnetic device and electric motor directly or indirectly through a mechanical transfer unit such as lever, cam and etc. An example is shown in Japanese Patent Publication No. 4135/1979.

[0076] In the embodiment, the variable displacement pump 10 used for oil pressure source of power steering system installed in vehicle is shown. However, the invention is not limited to this, and it is applicable that reliability on operation of apparatus using pressure fluid side is kept by increasing or decreasing supplying flow rate in response to necessity and pump power is reduced so as to show saving energy effect.

[0077] Although the metering throttle 50 comprising the fixed throttle is provided standing on the position facing to side wall side of the cam ring 17 in the embodiment, the invention is not limited to this, and the metering throttle may be provide at suitable position of the discharge side passage 27. In short words, fluid pressure of upper and lower stream sides of the metering throttle 50 may be conducted to both sides chambers 38 and 36 of the control valve 30.

[0078] Although the rod member 71 is provided connecting to the end portion of the spring chamber 36 side of the spool 32 in order to apply thrust of the solenoid 60 to the spool 32 of the control valve 30 to move to axis direction in the embodiment, this has the purpose sharing the spool 32 with pump of other type, and these may be connected integratedly by press fitting or may be formed integratedly. Further, a variation is considerable that the rod member 71 and the rod 65 of the solenoid 60 are formed in one body or integratedly and the end portion of the spool 32 and the rod member 71 are faced in almost contacting state.

[0079] As described above, according to the variable displacement pump of the invention, an electronic driving unit applying thrust to axis direction to the spool of the control valve is provided, therefore, the invention has the following superior advantages in spite of the simple structure.

[0080] That is, since pump discharge quantity can be made necessary minimum at non-steering such as straight travel according to the invention, power consumption can be saved. When pump discharge quantity such as while steering is necessary, force by the electronic driving unit acts directly on the spool of the control valve and necessary flow rate can be discharge quickly.

[0081] According to the invention, since the metering throttle is a fixed throttle having a certain opening area, differential pressure that the spool keeps balance state with the minimum flow rate at non-steering is small. Therefore, since pressure loss of fluid at the metering throttle in this state is small, power consumption of the pump can be further decreased.

[0082] According to the invention, since sum of thrust by the electronic driving unit and spring force of the control valve is same as spring force of the conventional control valve, smaller spring in spring force can be used as the spring for the control valve comparing with the conventional spring, and the control valve can be operated smoothly similarly as the conventional pump. Therefore, power consumption at pump driving is made necessary minimum and the maximum saving energy effect is obtained with low cost.

[0083] According to the invention, when an oil pressure pump for vehicle is used for oil source of steering system for example, since pump discharge quantity is controlled through the control valve by driving the electronic driving unit corresponding to condition such as speed of vehicle, steering speed and etc., suitable steering feeling is obtained fitting various travel state of the vehicle. 

What is claimed is:
 1. A variable displacement pump comprising: a rotor; a cam ring defining a pomp chamber between the rotor and the cam ring; a pump body holding the cam ring to move to a direction that a pump capacity of the pump chamber increases and decreases, the pump body defining a first and a second fluid pressure chambers at both sides of a moving direction of the cam ring; a control valve having a spool operated to an axis direction by difference in fluid pressure of upper and lower stream sides of a metering throttle formed on a way of a discharge side passage of the pump chamber, the control valve for controlling at least fluid pressure in the first fluid pressure chamber; and an electronic driving unit for applying thrust to the axis direction to the spool of the control valve.
 2. The variable displacement pump according to claim 1 , further comprising an electronic control unit for driving and controlling the electronic driving unit, wherein the electronic control unit includes a steering sensor for detecting a steering speed of a steering wheel, and the electronic control unit drives and controls the electronic driving unit according to a signal from the steering sensor.
 3. The variable displacement pump according to claim 2 , wherein the electronic control unit includes a speed sensor for detecting a travel speed of a vehicle, and the electronic control unit drives and controls the electronic driving unit according to a signal from the speed sensor. 